THE ANATOMY OF THE WEDDELL SEAL. 829 
of Sir Wo. Turner ®* in his account of the brain of the elephant seal, I propose to deal 
at some length with the arrangement of the convolutions and fissures and the possibility 
of dividing the cerebral surface into subordinate lobes, after the manner adopted in 
describing the human brain. 
The complexity of the convolution pattern of the brain of seals has led observers to 
devise such an elaborate terminology for the description of the separate convolutions 
and fissures that it is a matter of considerable difficulty to correlate the different terms. 
Consequently, bearing in mind the variations which specimens of these brains present 
among themselves, as well as their divergence from the ordinary type of carnivore brain, 
I have preferred to restrict the use of terms as much as possible, and to limit the attempt 
to establish homologies to such characters as were fairly comparable to those presented 
by the human brain. 
1. The Lateral Surface of the Hemisphere. (Fig. 1.) 
On this aspect the convolutions and fissures were well developed both as regards 
their size and their numbers, and yet any underlying “pattern” resulting from the 
disposition of the primary fissures was most elusive and difficult to decide. Fortunately, 
there was no uncertainty with regard to the fissure of Sylvius (sulcus Sylvii). Its 
commencement in relation to the locus perforatus anticus on the basal surface of the 
brain, and its position between the orbital and temporo-sphenoidal parts of the hemi- 
sphere on the same surface, fixed the position of its main stem without any doubt, and 
so by its outer end it provided one fixed point from which to unravel the complexity of 
the lateral surface. TurNneER found this fissure traceable on the lateral aspect of the 
hemisphere ‘“‘ upwards and backwards for 32 mm. on the side of the right hemisphere, 
but not so far on the left.” Nevertheless, for some time | found great difficulty in 
deciding which, and how many, of the fissures upon the lateral surface were entitled to 
be accepted as its direct continuations, althouch, as the dissection proceeded, the decision 
_arrived at in the first instance was verified as correct. My initial difficulty was increased 
by the fact that in the lateral view of the hemisphere of the brain of the dog, as may be 
seen in the figure given by WrepDERSHEIM and Parker,t the fissure of Sylvius is 
represented as a “‘ closed” fissure, 7.e. one provided with “ opercula,” forming an “ arcuate 
gyrus” which surrounds the fissure on all aspects except the basal segment of the 
fissure. Further, in the brain of the dog, this ‘‘arcuate gyrus” is repeated twice, so 
that altogether on the lateral aspect of its hemisphere, to quote WIEDERSHEIM and 
Parker, ‘“‘In carnivores, cetaceans, and ungulates, three gyri arch over the Sylvian 
fissure, one above the other, and are separated by the so-called arcuate fissures.” { 
Certainly this was not the manner in which the convolutions and fissures were disposed 
on the lateral aspect of the hemisphere of the Weddell seal in relation to the fissure of 
* Turner, Challenger Reports, vol. xxvi., Zoology; Report on Seals. 
+ WiepeRsHErm™M and ParkEr, Comparative Anatomy of Vertebrates, 3rd ed., 1907, p. 224, 
t Ibid., p. 228, 
